In a method of manufacturing a device case, plate members are welded to each other in some cases. More specifically, such a method includes bringing a second plate member as part of the device case into contact with an end of a first plate member as another part of the device case so as to be substantially perpendicular to the first plate member, and applying a welding focused beam to weld and fix the first plate member and the second plate member such that a welded portion is formed at a contact portion between the first plate member and the second plate member. In other words, the method of manufacturing the device case employs the welding technique of applying a focused beam to a portion to be welded so as to precisely control the position of the welded portion between the plate members.
More specifically, there has been known a method disclosed in JP-A-2004-195490 as one of the methods of manufacturing a device case with use of this welding technique. This method employs the so-called penetration welding technique. In this technique, an end of an upper wall (top plate) is mounted on an upper end of an upright wall, the contact portion therebetween is irradiated with a focused beam (laser beam) from above the top plate to generate a welded portion entirely across the width in the thickness direction of the top plate. The welded portion reaches an upper portion of the upright wall.
This penetration welding technique is advantageous in that the focused beam is not incident into the device case and the irradiated position does not have to be set so accurately, in comparison to a case of directly applying a focused beam to the contact portion between the upright wall and the top plate.